Structure of the ARS/Igh11 transgene and transgenic µ expression. (A) Heavy chain variable region and constant region coding segments are shown as gray rectangles. Both the intronic enhancer (between the VDJ and Cμ exons) and the 3′ enhancers are shown as black circles. “2X INS” indicates two copies of the chicken β-globin insulator. Expression of Cre from the EIIa Cre transgene results in deletion of the 28-kb region containing the four 3′ enhancers (A, bottom), but spares 15 kb of sequence that flank the 3′ end of the enhancer region. 761* was not established as paired transgenic lines. We had only a mother with intact genes and 761Δ offspring from her, and so could test these mice in only a single experiment. (B) Analysis of surface Ig expression by flow cytometry. Line 336 B cells were tested with a different concentration of anti-B220, resulting in a lower apparent surface expression. Expression in lines 234, 234Δ, 231, 231Δ, 761, and 761Δ was similar to surface Ig expression in line 336. (C) The relative surface transgenic IgMa expression in lines 820 and 820Δ, and 774 and 774Δ, is shown as histograms. (D) Transgenic VDJCµ expression, as determined by RT-PCR, using fivefold dilutions of cDNA. Each experiment shown was repeated in one or two additional experiments.
